[belorn]

There exist many utilities that themselves are built on top of other utilities.

The reason something should be an utility has to do with competition and how much power customers. The primary argument in favor of having Internet providers be an utility is that creating an competing Internet is not really an realistic concept, and the power customers of ISP has in their customer-provider relation is close to nothing. Utility laws exist to solve this specific situation in the market, and making every single company an utility would not be very efficient way to make use of those laws.